Dear Admed Billa
I have read the replies to your query regarding the City engine decreasing oil. Unfortunately, most are off the mark.
I reccomend to you that the vehicle is taken to the Honda Dealer and have his technicians inspect the engine.
A weak engine has many signs, for instance that idle may not be smooth, there may be clatter from the engine. Pick would suffer. Fuel consumption would go up etc. From your description I am inclined to believe that the engine of your frind's vehicle is not weak. In any case, your Honda 3s Technicians can perform a compression check and would tell you exactly what may or may not be wrong with your friends car.
A Catalytic Converter WOULD NOT catch the blue smoke that comes from a weak engine. So if the engine was blowing blue smoke, You would see it.
8000 Km interval is fine for a Honda City engine if the car is driven gently. SInce your friends likes to drive like a "maniac". I reccomend that the Oil is changed at the 5000km Interval.